There are a number of new microwave distribution systems under development using frequencies above 10000 MHz. Inter-satellite communications use the 28000 MHz frequency range. Multi-channel or interactive television would use the 27500-29500 MHz frequency range, while some wireless cable operators are opting for the 12 GHz CARS band. This activity has prompted a strong interest in base station antennas (similar to broadcast station antennas). The antennas need to operate over a fairly wide bandwidth with a moderate to high power input. The azimuth-plane coverage requirement, in most cases, is omnidirectional, while the elevation-plane coverage is specified (in various forms) for radiation towards the earth and is, usually, to be minimized towards the sky. The polarization may be either horizontal or vertical.
Omnidirectional antennas are traditionally linear arrays of basic radiating elements such as slots or dipoles. However, the requirement for broad band operation is not compatible with linear array technology. The problem is further complicated by the relatively high power requirements (up to 2 Kw) at these high frequencies.